ABC announced
Toscano will perform during the April 26 episode, while Ballas dances on the ballroom floor. "I'll be doing a regular results show," Ballas told press backstage after the April 19 episode. "I get to dance with
Karina [Smirnoff]. Pia is going to sing, which is going to be amazing. She's a ridiculously amazing vocalist."

"It's a first," Ballas says of the FOX star appearing on the ABC series before her season even ends -- though it's something he's quick to point out he had nothing to do with.

"We're not allowed to know stuff," he says, noting Pia's inclusion is entirely the producers' decision. "I can't get up and go, 'Can we get
John Mayer on the show this Tuesday?' We have no say whatsoever."

Ballas could not confirm the song or dance that would be a part of the performance, but he did say it would likely be "something slow."

His partner Chelsea Kane is excited for the crossover. "We hang out backstage, it's so funny," she says of their shared home at CBS Studios. "We'll be in the elevators, and it's just the Idols and the dancers."

Apparently it wasn't always so chummy. Earlier in their run, Ballas says things were a bit more tense sharing a space with "American Idol," sparing words in favor of posing like a one of the Sharks giving a Jet the skeptical up-down.